The invention relates to microelectromechanical devices.
In forming a well, many different types of operations may be performed, including drilling, logging, completion, and production operations. Various different types of devices are used to perform the desired operations. Examples of such devices include perforating guns to perform perforating operations, flow control devices to control fluid flow (injection or production), packers to isolate different regions of the well, and other devices.
The activating mechanisms to activate such devices may include mechanical, hydraulic, and electrical activating mechanisms. To electrically activate a downhole device, a power source is connected to the downhole device. This is typically accomplished by using switches, either at the surface or in a downhole module. The switch is initially open to isolate the power source from the downhole device. When activation is desired, the switch is closed to provide electrical power to the downhole device.
In wellbore applications, one type of switch is made from a gas discharge tube, also known as a spark gap switch, that is either a triggered-type or over-voltage type switch. A triggered-type switch employs an external stimulus to close the switch or to activate it. An over-voltage switch is activated whenever the voltage level across the switch exceeds a threshold value.
Some switches employ a gas tube having an electrode at each end. In order to make the switch conduct electrical current, either a trigger voltage is applied to a third electrode, or the switch is forced into conduction as a result of an over-voltage condition. Since the typical gas tube discharge switch is arranged in a tubular geometry, it is usually associated with a relatively high inductance because of relatively long conduction path lengths. Also, the tubular shape of a gas tube does not allow convenient reduction of the overall size of a switch. Additionally, it may be difficult to package and integrate the gas tube switch with other components.
Another type of switch includes an explosive shock switch. The shock switch is constructed using a flat flexible cable having a top conductor layer, a center insulator layer, and a bottom conductor layer. A small explosive may be detonated on the top layer causing the insulator layer to form a conductive ionization path between the two conductor layers. One variation of this is a “thumbtack” switch in which a sharp metal pin is used to punch through the insulator layer to electrically connect the top conductive layer to the bottom conductive layer. The thumbtack switch is similar to the explosive switch but it may not be reliable because, as it punches a hole, the “thumbtack” may simply bend the insulation layer along with it, so that the thumbtack may fail to make a connection between layers.
Switches can also be used in other applications and other fields, such as in military, medical, manufacturing, communications, computers, consumer electronics, construction, demolition, seismic, and mining applications to safeguard electronic components by quickly shunting dangerous voltage and current surges to ground, to activate electrical devices, or initiate explosive devices. Many such switches are associated with various shortcomings as described above.